Various means of administering drugs to the intestine are known. For example oral controlled release compositions are used to reach the upper part whereas enemas are used to reach the lower part. Enemas are usually used in the form of a foam to overcome the problem of leakage from the rectum following administration which makes it necessary for patients to lie down during administration. Foams, as well as pessaries, tampons and creams are used to administer drugs to the vagina.
Conventional foams for rectal or vaginal administration are filled in pressurised containers with a pharmaceutically active ingredient dissolved or suspended in a liquid vehicle, at least one propellant gas and a surfactant with foaming properties. Examples based on mesalazine, peppermint, sucralfate or budesonide as the active ingredient dispersed in a liquid vehicle containing a foaming surfactant and administered for topical action in the colon using a pressurised atomiser with a propellant gas are described in EP-A-468 555. Rectal foams formed by a propellant gas on expulsion from a pressurised container and containing other active ingredients such as flunisolide and its derivatives (see WO 94/12187), 5-aminosalicylic acid (EP 395 329), and 4-aminosalicylic acid (DE 4316724) have also been described.
Chlorofluorocarbons are generally used as the propellant gas but these are undesirable for environmental reasons. Also the use of pressurised containers to administer pharmaceutically active substances suffers from a number of problems. For example, it is difficult to administer an accurate dose of the pharmaceutical composition of the drug; the containers are difficult to store over long periods of time because of leakage of gas which results in reduced administration capacity. Furthermore the disposal of used containers can be dangerous because of the risk of explosions on incineration. Accordingly alternative formulations need to be found.